The present invention relates generally to data communications and more specifically to transmission and receipt of data via a linear broadband network.
There currently exists a complex and robust wired television cable infrastructure that is commonly referred to as the Hybrid Fiber Coax (xe2x80x9cHFCxe2x80x9d) network. The HFC network is an example of a linear broadband network having substantially linear and broadband frequency characteristics. A linear broadband network exhibits linearity in that there are substantially no exponential terms in a gain function of the network over a frequency band of operation. As one of ordinary skill in the art appreciates, an all fiber and an all coaxial cable network is also a linear broadband network. The HFC network merely happens to be the most prevalent linear broadband network in use at the time of the filing of the present patent application. The HFC network has typically been used for delivery of television signals to subscribers. Each subscriber, which represents either an individual or a business, is connected to the cable TV HFC network through coaxial cables running from a headend in a trunk and branch configuration to individual subscribers. Over time, the cable TV HFC network has been upgraded by replacement of some of the coaxial cable trunk lines with fiber optic cable, which has led to this infrastructure being referred to as the HFC network. The connection between the HFC network and the subscriber premises is conventionally made with a coaxial cable, referred to as a subscriber drop, which spans the connection between a tap connected to the HFC network and a client device, which is most cases is a television set, located in the subscriber premises.
Deregulation of the communications industry has made it permissible for the telephony companies to supply television and video services and cable companies to supply telephony and data services. Accordingly, there is an interest among the cable TV service providers to grow their market share by being able to offer all communications services. The cable TV service providers are in a unique position in that they already have a linear and broadband network that reaches many existing subscribers. Their main historical business being television delivery, the cable companies have focused primarily on the forward or downstream path. In order to be a full service provider, however, the return or upstream path from the subscriber to the headend must be provided. For example, there is a growing demand for communication services that require higher performance from the communication infrastructure, such as higher speed Internet access, interactive television, video conferencing, and telephony. As the demand grows, there will be increasing demands placed on the quality and speed of the downstream and upstream paths. Providing subscriber access to the upstream path presents a challenge to the cable TV service providers. The cable TV service providers have provided a high quality network up to the curb (tap). However, the subscriber drop and client devices have been a source of significant noise resulting from bad connectors, unterminated connections, frayed cables, faulty wiring, breached shielding, noise generated by subscriber appliances, etc. The noise leaks into subscriber wiring and onto the subscriber drop, presenting itself on the upstream path of the HFC network as unwanted signal energy. The very nature of the trunk and branch configuration of the hybrid fiber coax network causes the noise to accumulate on the upstream path as the branches of the network converge. The noise from each subscriber adds together to reduce the overall signal-to-noise ratio of the return signal.
The signal-to-noise ratio of a communications signal is directly related to the effective bandwidth of the channel. Decreasing the signal-to-noise ratio, therefore, increases the bit error rate of a channel. As signal-to-noise ratio decreases, the data transmission rate must slow to a level that provides a sufficiently low bit error rate. The lowering of the data transmission rate is in direct contravention to the objective of the cable TV service providers in supplying high-speed communication services. The signal-to-noise ratio problem is exacerbated when the composite signal reaches an optical laser that is used to power the return transmission fiber. The absolute power level of the signal is limited because the laser has a fixed modulation index. In other words, as the noise level increases, the available signal strength decreases. This limits the cable service provider""s option of amplifying the signal to achieve an acceptable signal-to-noise ratio. In data transmission applications, it is possible to employ loss packet retransmission to correct for noise that degrades the integrity of the upstream information. As speeds increase, however, retransmission consumes valuable bandwidth that would otherwise be used for additional upstream information. Consequently, noise limits the overall capacity of the network, thereby increasing the cost of the service to subscribers. There is a need, therefore, to improve upstream capacity on the network by reducing the injection of upstream noise.
U.S. Pat. No. 5,867,485 issued to Chambers et al. and assigned to Bellsouth Corporation, proposes a low power microcellular wireless drop for a full duplex interactive network in which a cable connecting a bi-directional fiber network to a subscriber premises is replaced by two wireless transceivers. A Network Interface Unit multiplexes and de-multiplexes signals transmitted and received from a number of subscriber appliances. These signals are transmitted and received by a roof or eaves mounted antenna. The upstream signal is up-converted, amplified, and filtered before being transmitted to a receiver. The system disclosed is a linear processing system, which amplifies the noise presented to the upstream path by the subscriber premises. Disadvantageously, the linear processing propagates any in-band noise and reduces the signal-to-noise ratio. The downstream signal is filtered, amplified, and down-converted before entering the Network Interface Unit and de-multiplexed to the appropriate appliance. The wireless drop succeeds in isolating the subscriber premises from the bi-directional fiber network, but does not remove the noise injected into the upstream signal. There remains a need, therefore, for a method or system to limit the noise ingress into the upstream path.
According to one aspect of an embodiment of the present invention, a method of communicating information from a client device to a linear broadband network having substantially linear and broadband frequency characteristics comprises the steps of generating an upstream baseband signal having a predefined format. The method further comprises modulating the upstream baseband signal onto at least one upstream wireless radio frequency carrier to generate at least one first upstream modulated carrier signal and transmitting the at least one first upstream modulated carrier signal wirelessly. The method further includes receiving the at least one first upstream modulated carrier signal at a network access interface device coupled to the linear broadband network and demodulating the at least one first upstream modulated carrier signal to produce an upstream demodulated baseband signal. The method then comprises modulating the upstream demodulated baseband signal onto at least one upstream linear broadband radio frequency carrier to produce at least one second upstream modulated carrier signal having a signal format compatible with the linear broadband network.
According to another aspect of the present invention, a method of communicating bi-directional information between a client device and a linear broadband network having substantially linear and broadband frequency characteristics comprises the steps of generating an upstream baseband signal, having a predefined format, and modulating the upstream baseband signal onto at least one upstream wireless radio frequency carrier to generate at least one first upstream modulated carrier signal. The method further comprises transmitting said at least one fist upstream modulated carrier signal wirelessly and receiving said at least one first upstream modulated carrier signal at a network access interface device coupled to the linear broadband network. The method further comprises demodulating the at least one first upstream modulated carrier signal to produce an upstream demodulated baseband signal and modulating the upstream demodulated baseband signal onto at least one upstream radio linear broadband frequency carrier to produce at least one second upstream modulated carrier signal having a signal format compatible with the linear broadband network. The method further comprises receiving at least one downstream linear broadband network radio frequency carrier signal comprising a first downstream modulated carrier signal from the linear broadband network and demodulating the at least one first downstream modulated carrier signal to produce at least one first downstream baseband signal having a predefined format. The method further comprises modulating the at least one first downstream baseband signal onto at least one downstream wireless radio frequency carrier to generate at least one second modulated downstream carrier signal and transmitting said at least one second modulated downstream carrier signal wirelessly. The method further comprises receiving the at least one second modulated downstream carrier signal and demodulating the at least one second modulated downstream carrier signal to produce at least one second downstream baseband signal. The method further comprises transmitting the at least one second downstream baseband signal.
According to another embodiment of a system for upstream communication, the system comprises a linear broadband network having substantially linear and broadband frequency characteristics, a first upstream modulator that modulates at least one upstream baseband signal received from a client device, the at least one upstream baseband signal being modulated onto at least one upstream wireless radio frequency carrier to produce a first upstream modulated carrier signal. The system further comprises an upstream transmitter that wirelessly transmits the at least one first upstream modulated carrier signal, an upstream receiver that receives the at least one first upstream modulated carrier signal, and an upstream demodulator that demodulates the at least one first upstream modulated carrier signal to generate at least one upstream demodulated baseband signal. The system further comprises, a second upstream modulator that modulates the at least one demodulated upstream baseband signal onto at least one upstream linear broadband network radio frequency carrier for transmission onto the linear broadband network.
According to another embodiment of the present invention a system is provided for bi-directional communication that comprises a bi-directional linear broadband network having substantially linear and broadband frequency characteristics, a first upstream modulator that modulates at least one upstream baseband signal received from a client device, the at least one upstream baseband signal being modulated onto at least one upstream wireless radio frequency carrier to produce at least one first upstream modulated carrier signal, and an upstream transmitter that wirelessly transmits the at least one first upstream modulated carrier signal to an upstream receiver. The upstream receiver receives the at least one first upstream modulated carrier signal. The system further comprises an upstream demodulator that demodulates the at least one first upstream modulated carrier signal to generate at least one upstream demodulated baseband signal. The system further comprises a second upstream modulator that modulates the at least one demodulated upstream baseband signal onto at least one upstream linear broadband network radio frequency carrier for transmission onto the linear broadband network. The bi-directional system further comprises a first downstream receiver that receives at least one first downstream modulated carrier signal from the linear broadband network, a first downstream demodulator that demodulates the at least one first downstream modulated carrier signal to produce a first downstream baseband signal, and a downstream modulator that modulates the first downstream baseband signal onto a downstream wireless radio frequency carrier to produce a second downstream modulated carrier signal. The system further comprises a downstream transmitter that transmits the downstream modulated carrier signal, a second downstream receiver that receives the downstream modulated carrier signal, and a second downstream demodulator that demodulates the downstream modulated carrier signal to produce a second downstream baseband signal for delivery to the client device.
In another embodiment according to the teachings of the present invention, an apparatus for coupling to a linear broadband network is provided that comprises an upstream receiver that wirelessly receives at least one first upstream modulated carrier signal, an upstream demodulator that demodulates the at least one upstream modulated carrier signal to produce at least one demodulated upstream baseband signal, an upstream modulator that modulates the at least one demodulated upstream baseband signal onto at least one upstream linear broadband network radio frequency carrier to produce at least one second upstream modulated carrier signal for transmission on the linear broadband network, and an upstream transmitter that transmits the at least one second upstream modulated carrier signal onto the linear broadband network.
In another embodiment according to the teachings of the present invention, an apparatus is provided for communicating with a linear broadband network having substantially linear and broadband frequency characteristics comprises an upstream receiver for receiving a plurality of upstream baseband signals over a wired connection from a plurality of client devices, a multiplexer for multiplexing the plurality of upstream baseband signals onto a multiplexed upstream baseband signal, a first upstream modulator for modulating the at least one multiplexed upstream baseband signal onto at least one upstream wireless radio frequency carrier, and an upstream transmitter for transmitting the at least one upstream wireless radio frequency wireless carrier.
In another embodiment according to the teachings of the present invention, a system is provided for upstream communication over a linear broadband network having substantially linear and broadband frequency characteristics, comprises a subscriber access interface device that receives an upstream baseband signal from a client device, modulates said upstream baseband signal onto at least one upstream wireless radio frequency carrier to produce at least one first upstream modulated carrier signal, and wirelessly transmits the at least one first upstream wireless modulated carrier signal, and a network access interface device, coupled to said linear broadband network, that receives the at least one first upstream modulated carrier signal, demodulates the at least one first upstream modulated carrier signal to produce at least one demodulated upstream baseband signal, modulates the at least one demodulated upstream baseband signal onto at least one upstream linear broadband network radio frequency carrier having a format compatible with the linear broadband network to produce at least one second upstream modulated carrier signal, and transmits the at least one second upstream modulated carrier signal onto the linear broadband network.
In another embodiment according to the teachings of the present invention, a system is provided for upstream communication comprises a linear broadband network having substantially linear and broadband frequency characteristics, a subscriber access interface device that receives an upstream baseband signal from a client device, modulates the upstream baseband signal onto at least one upstream wireless radio frequency carrier to produce at least one first upstream modulated carrier signal, and wirelessly transmits the at least one first upstream wireless modulated carrier signal. The system further comprises a network access interface device, coupled to the linear broadband network, that receives the at least one first upstream modulated carrier signal, demodulates said at least one first upstream modulated carrier signal to produce at least one demodulated upstream baseband signal, modulates said at least one demodulated upstream baseband signal onto at least one upstream linear broadband network radio frequency carrier having a format compatible with the linear broadband network to produce at least one second upstream modulated carrier signal, and transmits the at least one second upstream modulated carrier signal onto the linear broadband network.
In a system employing a method according to the teachings of the present invention, noise that accumulates at the subscriber premises is removed from the upstream signal prior to presentation of the signal to the upstream path of the linear broadband network. Because the upstream signal generated is a digital signal or an analog signal that has been converted to a digital signal, when the carrier is demodulated, the system is able to reconstruct the signal into an image of the transmitted digital signal without the noise, thereby restoring the information integrity of the original signal. The inherent bandwidth limiting function and hysterisis of a digital signal filters out and removes much of the noise, as the signal is prepared for transmission. A baseband signal directly modulates a wireless carrier using modulation techniques that minimize noise interference of the transmitted signal. The reconstruction process further filters out noise that is injected into the system because of the transmission process. Advantageously, this elimination of noise is cumulative and provides for a significantly quieter upstream path composite signal.
Use of a digital baseband signal for the entire distance up to wireless transmission greatly reduces the introduction of noise and permits use of error checking and retransmission, forward error correction, error concealment, or a combination thereof in the link between the subscriber premises and the network access interface device. Similar use of error checking and retransmission, forward error correction, and error concealment may also be used for the link between the network access interface device and the headend. The additional error management step advantageously reduces the number of errors that must be addressed allowing faster data transmission rates and more efficient use of bandwidth as compared to conventional systems.
As pointed out above, the linear broadband network communications infrastructure may comprise the hybrid fiber coaxial (xe2x80x9cHFCxe2x80x9d) network conventionally used for delivery of cable TV services. The HFC network currently uses a wired tap technology. The wired tap technology comprises a drop cable extending from a tap at a curb to equipment located at a subscriber premises. The wireless tap, or network access interface device according to the teachings of the present invention, is compatible with and is able to coexist on the same network as the wired tap. Accordingly, the network access interface device of the present invention provides a smooth and gradual upgrade installation path for communication service providers. Services to existing subscribers need not be disturbed when subscribers are added or upgraded. Each network access interface device supports a plurality of subscribers. Accordingly, the total number of two-way transceivers connected to the linear broadband network is reduced. By concentrating the services supported by a single modem, there is a decrease in the number of noise sources connected to the linear broadband network. The signal-to-noise ratio, therefore, is improved by 10 log the a ratio of the number of network access interface devices over the number of wired modems that a conventional system would require for the same level of service.